Corrective Tasks

Corrective maintenance consists of the action(s) taken to restore a failed component to operational status. Corrective maintenance is performed at unpredictable intervals because a component's failure time is not known a priori.

Corrective tasks:

• Always bring the block down.
• May bring the system down.
• Require spare parts.

In addition to the common task properties, the following options are used to configure corrective tasks in the Maintenance Task window:

• Task Scheduling allows you to specify when the corrective task will be performed.
  • If you choose Upon item failure, the task will be initiated upon failure of the component.
  • If you choose When found failed during an inspection, the task will be initiated if the component is found to be failed at the next scheduled inspection. This is useful in the case of "hidden failures" (i.e., failures that are not apparent until an inspection is performed) and in cases where the component is not considered mission critical and repair can wait until the next scheduled maintenance.
    • If a preventive task takes place before the next inspection, then preventive maintenance (not corrective maintenance) will be performed to restore the block. The downtime, etc. will depend on the preventive task properties.
    • If a corrective task is performed upon inspection and an inspection finds the block failed, then the total downtime includes the full inspection duration followed by the corrective task duration.

If you have selected to perform a corrective task upon inspection and an inspection or preventive task does not occur after the failure, then the block will never be restored. This could happen under either of the following circumstances:

• Neither an inspection nor a preventive task is specified for the block.
  
  and/or
• The conditions have not been met to perform an inspection or preventive task.
• Basic Repair Properties > Spare Part Pool allows you to choose or create the spare part pool(s) that will be used in performing the task. A spare part pool describes the conditions that determine whether a spare part will be available when needed and specifies the time and costs associated with obtaining the spare part. If a spare part pool is not assigned, it is assumed that unlimited free spares are always immediately available.
  
  You must specify a quantity of parts requested from the pool by the task. All requested parts must be delivered before the task can be performed. The default value in the Quantity requested by task field is 1.
  
  You can assign multiple spare part pools to a task. In this case, the task is assumed to require all requested parts from all requested pools. In other words, the pools are in an AND relationship, not an OR relationship.
  
  For corrective and preventive tasks, the simulation requests a team as soon as a task is initiated; however, the team does not begin performing the task unless/until all required spare parts are available.
  
  The total time for the task consists of:
  • The time to complete corrective and preventive maintenance (based on the corrective task or preventive task properties).
    
    PLUS
  • The longer of the following times:
    • The time to obtain all spare parts (based on the spare part pools).
      
      OR
    • The time to obtain an available crew (based on crew availability) and any logistical delay time associated with the crew.

For example, consider a block that fails at 10 hours (on the system clock). Its corrective task will take 5 hours, the time required to obtain all spares will be 48 hours and the team consists of a single crew with a logistical delay time of 8 hours. In this case:

• All spares will arrive by 58 hours (on the system clock).
• The team will be requested at 10 hours and will arrive at 18 hours (on the system clock).
• The maintenance will be completed at 63 hours (on the system clock).
• The total time for the corrective maintenance will be 53 hours (48 for the spares plus 5 for the task).
• The team's crew will have traveled for 8 hours, waited 40 hours for the spare parts and performed the task for 5 hours for a total of 53 hours (including waiting for the spare parts).

If the spare parts are available without delay and all other conditions are the same, then:

• The team will be requested at 10 hours and will arrive at 18 hours (on the system clock).
• The maintenance will be completed at 23 hours (on the system clock).
• The total time for the corrective maintenance will be 13 hours (8 for the team plus 5 for the task).
• The team's crew will have traveled for 8 hours and performed the task for 5 hours, for a total of 13 hours.
• Task Consequences
  • Does this task bring the system down?: By default, corrective tasks will not bring the system down unless having the block down brings the system down based on the reliability-wise configuration in the diagram. If you answer Yes, the task will bring the system down even if the task has a zero duration. This forces the task to be included in the count of system downing events, regardless of the task's duration.
  • Does this task bring the item down?: It is assumed that a block will always be down when a corrective task is performed, even a task with a zero duration; thus, this option cannot be changed.